With the continuous increase of the number of subscribers of mobile communication operators and amounts of services such as user voice data and so on, the infrastructure investment and deployment scale of mobile communication networks of the mobile communication operators must be correspondingly increased, and radio coverage and system capacity are continuously increased as well. By taking most mobile communication operators in Europe as an example, they successively deploy mobile communication systems (which belong to the 3GPP communication system family) of three different types of Radio Access Technology RAT systems, i.e., Global System of Mobile communication GSM, Universal Mobile Telecommunications System UMTS and Long Term Evolution LTE. In order to enhance various mobile communication functions and expand the system capacity, the above-mentioned three types of systems experience respective 3rd Generation Partnership 3GPP standardization technology evolution. In addition, the mobile communication operators widely deploy and use the Wireless Local Area Network WLAN system (which is evolving towards High Efficient WLAN HEW) in the IEEE communication system family as an efficient and low-cost capacity supplementation.
Any one of the mobile communication systems basically consists of the following main logic network element nodes: User Equipment UE of a single-mode or multimode system/Stationary Access STA, Radio Access Network RAN/Access Point AP, Core Network CN, Operation and Maintenance Center OMC, Transport Bearer Network TBN, etc. For example, a network side of the UMTS consists of a core network unit, Mobile Switching Center MSC/Medial GateWay MGW/Serving GPRS Support Node SGSN/Gateway GPRS Support Node GGSN, and a radio access network unit, NodeB/Radio Network Controller RNC, and 3GPP standardized terrestrial interfaces Iu, Iub and Iur therebetween, and so on. A network side of the LTE system consists of a core network unit, Mobility Management Entity MME/Serving Gateway SGW/Packet Gateway PGW/IP Multimedia Subsystem IMS, and a radio access network unit, Evolved NodeB eNB, and terrestrial interfaces S1 and X1 therebetween, and so on. A network side of a WLAN system consists of an Access Controller AC and a radio access unit AP and so on. Since the above-mentioned various systems Multi-RAT are evolutionary, coexists and provides jointly service in the long term, in order to enhance the cross-system performance, enhance the user experience of mobile communication, reduce software and hardware costs and facilitate the management and operation maintenance performed by operators, system manufacturers often couple the above-mentioned various systems to different extents to form so-called cross-system interoperation or joint operation. FIG. 1 illustrates a schematic diagram of a WLAN/3GPP interoperation coupling architecture in the related art, and the joint operation is as illustrated by the architecture example in FIG. 1. That has the beneficial effects that different RATs can exert the advantageous features of respective systems, different RATs can evenly share the communication loads of vast users, different RATs can form resource, coverage and capacity complementation. Thus a high-performance communication Key Performance Indicator KPI can be provided for the entire large system, and better mobile communication Quality of Experience QOE can be brought to users.
According to technologies which have already been disclosed and are discussing at current, a UE having a WLAN/3GPP multimode capability can be simultaneously in a state of communication connections with certain RAT networks in WLAN and 3GPP families. For example, a certain UE having a WLAN/LTE dual-mode capability is simultaneously under the coverage of radio signals of WLAN/LTE networks. The UE firstly establishes a Radio Resource Control RRC connection with the LTE network at a certain moment to perform a bidirectional communication of a certain IP service flow A, and thereafter a user initiates a new IP service flow B. In a user manual control mode, the UE searches for and finds WLAN coverage signals and completes necessary network access registration Attach (the process is called as WLAN network selection and registration). Then a CN which is integrated with various system core network functions may migrate the IP service flow B to the WLAN system to which the UE was successfully registered before according to certain policy and rule. Thereafter the IP service flow A of the UE is still born in the LTE network, and the IP service flow B is born in the WLAN network (the process is called as WLAN data flow offloading). FIG. 2a illustrates a schematic diagram of a state before an IP flow is offloaded to a WLAN network in the related art, FIG. 2b illustrates a schematic diagram of a state after an IP flow is offloaded to a WLAN network in the related art, and the above-mentioned processes are respectively as illustrated in FIG. 2a and FIG. 2b. 
In addition to WLAN network selection and data flow offloading between WLAN/3GPP, UE also simultaneously executes a mobility process in a 3GPP system according to the mobility feature in a physical space of the UE, e.g., reselection and handover of a serving cell. By taking cross-eNB handover of UE in the LTE system as an example (at the moment UE is in an RRC_Connected mode), FIG. 3a illustrates a schematic diagram when UE moves between source/target LTE cells and there is no WLAN coverage or data flow offloading in the related art. As illustrated in FIG. 3a, when the UE is located at the edge of an LTE cell A (since there is no coverage of any WLAN AP, no WLAN network selection and data flow offloading occur at all) and moves to an LTE cell B, a source eNB transfers a control right of RRC connection/E-RAB radio bearer to a target eNB according to a specific LTE mobile process. After a success is made, the LTE cell B will become a new serving cell of the UE. In a scenario which is a little more complex than the scenario illustrated in FIG. 3a, FIG. 3b illustrates a schematic diagram when UE moves between source/target LTE cells and there are WLAN coverage and data flow offloading in the related art. As illustrated in FIG. 3b, when the UE is located at the edge of an LTE cell A (since there is proper WLAN AP coverage, WLAN network selection and data flow offloading occur simultaneously) and moves to an LTE cell B, a source eNB also transfers a control right of RRC connection/E-RAB radio bearer to a target eNB according to a specific LTE mobile process. After a success is made, an LTE cell B will take over to become a new serving cell of the UE; and if at the moment the UE is still under the coverage of WLAN AP, WLAN network selection and data flow offloading may be continuously performed. As compared with the simpler scenario illustrated in FIG. 3a, in the scenario illustrated in FIG. 3b, since the UE is simultaneously in a WLAN data flow offloading state in a moving process in the 3GPP system, the source and target eNBs do not know the flow offloading state and the specific situation of the UE according to the current related art, and the following technical problems may be caused:
1. Since the target eNB does not know whether the UE is in the WLAN data flow offloading state before at all and does not know the situations of the volume and throughput of data transmitted at the WLAN side, in a process of making a handover preparation for the UE, more accurate resource reservation cannot be performed for the UE, and relative rough resource reservation may be performed only according to QOS related parameters of the UE such as the volume and throughput of the data transmitted in the source eNB. Consequently, if the UE successfully completes handover and the data at the WLAN side at first immediately flow back to LTE, the target eNB must perform additional allocation of resources again to serve for the transmission of the data which newly flow back. The two-time allocation process will increase the signaling overhead of an air interface and may interrupt or delay experience of some existing services to a certain extent.
2. Supposing that the target eNB always defaults that the UE is in the WLAN data flow offloading state and always performs additional resource reservation of a certain upper limit for the UE in the process of making a handover preparation for the UE. Once the data at the WLAN side actually flow back to LTE after the UE successfully completes handover, the target eNB can make the greatest effort to serve for the transmission of the data which flow back to a certain extent. However, if the UE originally is not in the WLAN data flow offloading state or no data backflow occurs after handover, the additional resource reservation performed by the target eNB is obviously useless and wasteful, which will cause some influences on normal services of other UE.
3. Since data transmission in the WLAN system is based on a mechanism of random competition between a plurality of users for radio resources, communication experience of each user, e.g., performance in aspects such as data transmission throughput, data packet delay and packet loss rate and so on cannot be guaranteed, and is usually and easily influenced by various objective conditions, and the UE can only make the greatest effort. For example, in the scenario illustrated in FIG. 3b, before handover, the average data transmission throughput of the IP service flow of the UE at the WLAN side may be relatively great or is in a trend of decrease, and after handover, due to the change of the radio condition, the UE is triggered to search for and reselect a network to load off the flow to another new WLAN which has heavier loads or is physically far away from the coverage of the old WLAN, and consequently the average data transmission throughput of the corresponding IP service flow becomes very small. If the target eNB can judge the situation of the change trend of the data transmission throughput of the UE at the WLAN side, it is possible to migrate all or partial IP service flow of the UE at the WLAN side back to the target cell B as soon as possible to maintain or improve the smooth experience of certain existing important services of the user.
The above-mentioned scenarios and problems may also be extended to cell reselection in the 3GPP system (at the moment the UE is in an RRC_Idle mode or there are additional Cell_FACH/PCH states and the like under the UMTS system), cross-system LTE<->UTMS inter-cell handover (at the moment the UE is in the RRC_Connected mode or in a corresponding Cell_DCH state under the UMTS), etc. In short, the target serving cell cannot know the WLAN-side data flow offloading state of the UE in the source serving cell and the specific situation of transmission experience in the moving process of the UE. Therefore, reasonable resource pre-configuration cannot be performed for the movement process, consequently the resource allocation and utilization efficiency in the 3GPP system is low; the existing services of the user may be released partly since the target cell takes over the control; the data transmission throughput fluctuates greatly and the consistency experience is relatively poor.
However, no effective solution has already been put forward aiming at the problem that the WLAN-side data flow offloading state of the UE and the situation of transmission experience cannot be obtained in the moving process of the UE in the related art.